The increasing printing speeds of copying machines, printers and the like each year are demanding corresponding improvements in toners and binder resins as well. For example, the toner and carrier must be violently agitated together to match the printing speed when electrostatic charges are generated the developing process, while lower fixing temperatures are also being used for the fixing process. In other words, with lower fixing temperatures there are required toners and toner resins with improved low-temperature fixing properties, improved electrostatic stability for more stable images, and improved blocking resistance so that the toner does not cake during storage.
In order to lower the fixing temperature and improve the fixing properties, it is necessary to reduce the molecular weight of the resin. Lower molecular weights, however, have led to problems of poor non-offsetting properties, as well as additional problems including lower glass transition temperatures and poor blocking resistance of the resins.
In the case of styrene/acrylic acid or methacrylic acid ester-based resins, reduction in the molecular weight necessitates a higher polymerization temperature during the production process, and when it is attempted to obtain the resin by suspension polymerization, a higher polymerization temperature causes the polymer to rise to the surface of the reaction solution due to the reaction pressure, generating what is known as a floating polymer, and producing a secondary cohesion polymer. Consequently, methods which use large amounts of a dispersant are employed to prevent the production of such secondary cohesion, but in such cases the large amount of dispersant used results in the problem of inferior image stability of the toner, while a large amount of the dispersant also adheres to the surface of the polymer which has undergone secondary cohesion, thus complicating its cleaning and removal, and also adding to the problem of inferior image stability.